In recent electrophysiological studies I have established that the olfactory and gustatory receptors of channel catfish, Ictalurus punctatus, are highly sensitive to specific amino acids and derivatives and have similar concentration-response function. However, the two systems differ with regard to phasic-tonic response characteristics, thresholds, and relative amino acid effectiveness. In this project I will examine catfish gustatory single fiber responses to the same and related compounds and classical taste stimuli. These data will be compared with the previously obtained gustatory whole nerve and twig averaged neural responses to determine how unit responses contribute to the population response. Cross adaptation studies will be performed to selectively adapt the olfactory and gustatory systems to specific amino acids and derivatives. This will be informative about similarities among stimuli and between systems in the transduction mechanisms leading to the neural response, and may possibly provide information concerning specific membrane receptor sites. Peripheral responses to stimulus mixtures will be compared to those obtained from the individual compounds contained in the mixture. Secondary olfactory responses will be compared to simultaneously recorded receptor responses which will be informative about central processing primary olfactory information. Effects of pH on olfactory and gustatory responses will be studied. These procedures will lead to a better understanding of the distinctions between taste and smell in catfish and may offer some insight into stimulus and coding mechansims.